Coaxial cables are widely used to carry high frequency electrical signals. Coaxial cables enjoy a relatively high bandwidth, low signal losses, are mechanically robust, and are relatively low cost. One particularly advantageous use of a coaxial cable is for connecting electronics at a cellular or wireless base station to an antenna mounted at the top of a nearby antenna tower. For example, the transmitter located in an equipment shelter may be connected to a transmit antenna supported by the antenna tower. Similarly, the receiver is also connected to its associated receiver antenna by a coaxial cable path.
A typical installation includes a relatively large diameter cable extending between the equipment shelter and the top of the antenna tower to thereby reduce signal losses. For example, CommScope, Inc. of Hickory, N.C. and the assignee of the present invention offers its CellReach.RTM. coaxial cable for such applications. The cable includes a smooth wall outer conductor which provides superior performance to other cable types. The smooth outer wall construction also provides additional ease of attaching connector portions to the cable ends in comparison to other coaxial cable types, such as including corrugated outer conductors, for example.
Each end of the large diameter coaxial cable is connected to a respective smaller diameter, and relatively short, jumper cable. The jumper coaxial cable has a smaller diameter with greater flexibility to thereby facilitate routing at the equipment shelter and also at the top of the antenna tower. More particularly, a relatively large diameter (about 1 and 5/8 inch) main coaxial cable extends from the shelter to the top of the tower, typically about 90 to 300 feet, to reduce attenuation. The main cable may be a CellReach.RTM. model 1873 cable, for example. A short smaller diameter (about 1/2 inch) coaxial jumper cable is connected to each end of the main cable, and may be a CellReach.RTM. model 540 cable, for example. The top jumper is typically 3 to 6 feet long, and the bottom jumper is typically 6 to 10 feet long.
At present, and as understood with reference to the prior art arrangement shown in FIGS. 2 and 3, first and second connectors 33, 34 are typically assembled in a back-to-back relation to couple an end of the main coaxial cable 31 to an end of a jumper coaxial cable 32. The first connector 33 includes a first back-nut assembly 35 and a first body portion 36 which are threadingly engaged together. A rear 0-ring, not shown, may seal the cable sheath 54 to the first back-nut assembly 35. Similarly, the second connector 34 includes a second back-nut assembly 41 which threadingly engages a second connector body portion 42. As shown in the illustrated prior art connector arrangement 30, the first or main cable 31 includes an elongate central strength member 43, a surrounding dielectric layer 45, and a surrounding adhesive layer 46 for attachment to the tubular copper center conductor 47. A tubular dielectric layer 48 surrounds the center conductor 47. In the illustrated embodiment, a portion of the dielectric layer 48 has been removed by a coring tool to thereby facilitate assembly. A tubular plastic body 51 is inserted into the cored cable end.
A portion of the outer smooth wall conductor 53 is exposed beyond the end of the cable sheath 54. A metal clamping ring 56 is urged against the exposed outer conductor 53 as the back-nut outer cylinder 55 is threaded onto the connector body portion 36. The connector body portion 36 includes a hollow metal member 57 in which is positioned an annular dielectric spacer 61, which, in turn, supports a center contact 62. The center contact 62 includes a tubular proximal end which receives and establishes contact with the inner conductor 47. An annular dielectric body 63 provides a radially compressive force to the tubular end 63 of the center contact 62 as the back-nut 35 and connector body portion 36 are threadingly engaged. A rubber 0-ring 67 seals the interface between the first back-nut assembly 35 and the connector body portion 36. A distal end 65 of the center contact 62 is centered within a hollow tubular distal end 66 of the hollow metal member 57. The distal end 66 includes threads on its outer surface to mate with the second connector body portion 42. Another 0-ring 94 is positioned at the distal end 66 for sealing the interface with the hollow metal member 85.
Turning now to the right-hand portion of FIG. 3, the second connector 34 is briefly described. The second connector 34 includes a second back-nut assembly 41 which is connected to the end of the second or jumper cable 32. The second cable 32 includes a central metallic conductor 71, surrounded by a dielectric layer 73, a portion of which is removed to prepare the cable end. A plastic insert 74 is positioned within the cable end to support the outer conductor 75. A cylindrical member 77 is secured on the cable end and clamps to an exposed portion of the outer conductor 75 which extends outwardly beyond the end of the cable sheath 76. Additional metal rings 81, 82 and 83 cooperate with the second connector body portion 42 and cylinder 77 to provide the necessary clamping action on the outer conductor 75 and also on the inner conductor 71. A rear 0-ring, not shown, may seal the cable sheath 76 to the second back-nut assembly 41.
The second connector body portion 42 includes a hollow metal member 85 which mounts an annular dielectric spacer 86 and which, in turn, carries a center contact 87. The center contact 87 includes a tubular distal end 88 which receives and is clamped against the inner conductor 71 by the annular dielectric body 90. An 0-ring 91 seals the interface between the second connector body portion 42 and the second back-nut assembly 41. A collar 92 including internal threads on its distal end is rotatably connected at its proximal end to a recess in the distal end of the hollow metal member 85. The collar 92 secures the first connector 33 to the second connector 34. The distal end 93 of the center contact 87 engages the distal end 65 of the center contact 62 in the region of the collar 92.
As will readily be appreciated, the back-to-back connector arrangement 30 includes a relatively large number of component parts which is relatively expensive and may be difficult to assemble. Such an arrangement 30 will also typically have more loss per unit length than the coaxial cable. Such a back-to-back connector arrangement 30 can be unreliable, and presents multiple interfaces for water leakage into the cable. The connector arrangement 30 also presents a number of abrupt edge surfaces which may make routing through restricted openings difficult, such as at the tower entry and exit ports, or at collars at spaced heights within a monopole tower.
A number of patents disclose other arrangements of connectors for securing a larger diameter coaxial cable to a smaller diameter coaxial cable. For example, U.S. Pat. No. 4,853,656 to Guilou et al. discloses such a device. The device comprises a central core in the shape of a truncated cone, whose circular bases have sections respectively identical to those of the central cores of the coaxal cables to be connected together, as well as a peripheral sheath, whose internal wall is a truncated cone shaped surface, whose circular bases have sections respectively identical to the internal sections of the peripheral sheaths of the coaxial cables. The small bases of the truncated cones of the central core and the peripheral sheath are two parallels of a first sphere centered on the apex of the truncated cone surface of the internal wall. The large bases of the truncated cones of the central core and of the peripheral sheath are two parallels of a second sphere concentric with the first one. This arrangement is disclosed for enhancing the propagation of electromagnetic waves through the device. Unfortunately, this device is also relatively complicated and difficult to assemble. In addition, a number of threaded interfaces are present which may permit water to enter the device and thereby reduce its reliability.